“The press spoke then of suicide, but in the essence, it is not. It is not even a protest,” Thich Nhat Hanh wrote of the monks, adding that “to burn oneself by fire is to prove that what one is saying is of the utmost importance. There is nothing more painful than burning oneself. To say something while experiencing this kind of pain is to say it with utmost courage, frankness, determination, and sincerity.”

David Buckel, a prominent civil rights lawyer turned environmental advocate, also set himself on fire in Brooklyn’s Prospect Park in 2018 to protest climate change and died. In a letter beforehand, Mr. Buckel alluded to the spiritual roots of self-immolation in protests, including in Tibet.

Mr. Bruce had, on his own Facebook page nearly three weeks before his act, recently edited a 2021 comment — under his post in 2020 warning of “irreversible” climate change — to include the date of his planned self-immolation, with a fire emoji. The apparent announcement of his plans was buried in his account timeline.

Other posts from Mr. Bruce’s Facebook account going back to April 2020 criticized “war profiteers,” President Donald J. Trump and collective inaction in the face of a worsening climate crisis. He also praised the young climate activist Greta Thunberg, quoted Dr. King, and as recently as March spoke of the “compassion” of Ukrainian refugees.

Dr. Kritee said that the last time Mr. Bruce had communicated with her was in a Facebook message he had sent in January, asking if she had seen his post about Ms. Thunberg. She added that if she or any other Buddhist teacher in Boulder had known of his plan to set himself on fire, they would have discouraged him from doing so.

There have been previous instances of public self-immolation in Washington. Arnav Gupta burned himself in front of the White House in 2019 and later died of his injuries. A motive in that case was never determined. Mohamed Alanssi, a Yemeni-born F.B.I. informant, set himself on fire outside the White House in 2004 in protest of his treatment by the government, but he survived. Norman R. Morrison, a Quaker man, burned himself to death outside the Pentagon in 1965 in protest of the Vietnam War.